Booster brake mechanism



Nov. 10, 1953 w. sTELzER BOOSTER BRAKE MECHANISM 3 Sheets-Shed?, l

Filed March 22. 1950 @Yami @IFAI/lz, a 4| 2 www wm WML/AM STE/ ZEE Nov. 10, 1953 w. sTELzER 2,658,348

BOOSTER BRAKE MECHANISM Filed March 22, 195o s sheets-sheet 2 ATTORN EY Nov. 10, 1953 I w, sTELzER 2,658,348

BOOSTER BRAKE MECHANISM 3 Sheets-Sheet 3 Filed Maoh 22. 1950 2,9 zzo zz/ WILL/AM STEL ZE E Patented Nov. 10, 1953 UNITED STATES PATENT OFFICE BOOSTER BRAKE MECHANISM William Stelzer, Summit, N. J.

Application March 22, 1950, Serial No. 151,119

11 Claims.

This invention relates to a hydraulic booster brake mechanism.

In the now commonly employed booster brake mechanisms, a fluid pressure motor is utilized to assist the operator in generating relatively high hydraulic pressure for applying the brakes. 'I'he motor partakes of a follow-up action relative to displacement of fluid from the master cylinder by the operator, and this follow-up action is accomplished in the prior art in either of two ways, namely, by hydraulic pressures developed by the operator, or by mechanical movement of some part actuated as a result of operation of the brake pedal.

Prior devices of the character referred to have been found to be practicable, but the follow-up action of the fluid pressure motor leaves much to be desired in the way of smoothness and accuracy. Moreover, the brake applying pressures developed by prior constructions have been higher than the pressure developed manually by the operator, and any fluctuation in the braking pressure due to even minor inaccuracies in the follow-up action of the booster motor has reacted through the manually operated parts of the mechanism to be felt by the foot of the operator.

It is well known that master cylinder piston diameters are compromises due to the fact that the displacement of the manually operable master cylinder piston cannot be sufficiently great to provide the volume of fluid necessary for moving the brake shoes into engagement with the drums and at the same time provide the degree of pressure necessary for full brake application.

An important object of the present invention is to provide a novel booster motor follow-up control mechanism which functions in accordance with the volume of fiuid displaced manually by the operator in a novel manner, instead of depending upon pressure fluctuations or distance of movement of a manually operable part, thus providing a more accurate follow-up action.

A further object is to provide such a mechanism wherein the operator in depressing the brake pedal performs two functions, namely to displace fluid at high pressure for brake application and to displace uid at negligible pressure to provide the volume of iiuid necessary for operating the booster motor mechanism, which functions to provide the substantial volume of fluid necessary for moving the brake shoes into engagement with the drums, thus permitting the use of a small operator-actuated piston for de- 2 veloping high braking pressures without the use Of substantial force on the brake pedal.

A further object is to provide a brake mechanism of the character referred to wherein the maximum braking pressure is the pressure developed by the operator, thus eliminating the subjection of the manually operable parts to pressures which are substantially higher than the manually generated pressures, by reason of which iiuctuations in brake pressures in prior mechanisms have reacted to the brake pedal, thus materially affecting the smoothness of operation of mechanisms of this character.

A further object is to provide such an apparatus wherein the dual iluid displacement effected by operation of the brake pedal does not add to the work which must be performed by the operator, and wherein such dual displacement may be accomplished by a particular type of master cylinder construction, or by a conventional master cylinder with the means built into the booster unit for effecting the manually controlled movement of fluid for operating the valve mechanism.

Other objects and advantages of the invention will become apparent during the course of the following description.

In the drawings, I have shown two embodiments of the invention. In this showing,

Figure 1 is an axial sectional View through the booster unit, the vacuum source, wheel cylinders and master cylinder being diagrammatically represented together with the piping connections associated therewith,

Figure 2 is an enlarged central vertical sectional view through the special master cylinder used in connection with the booster unit shown in Figure l,

Figure 3 is a sectional view similar to Figure 1 showing a modified form of the invention for use in conjunction with a conventional master cylinder as illustrated, a portion of the booster casing structure being shown in elevation,

Figure 4 is an enlarged detailed sectional view on line 4 5, of Figure'l, and

Figure 5 is an enlarged fragmentary face View of a portion of the casing structure.

Referring to Figure l, the numeral Iii designates the booster motor as a whole comprising casing sections II and I2 having a diaphragm I3 clamped therebetween in a manner to be described to form a constant pressure chamber I4 and a variable pressure chamber I5. The casing section II is provided with a nipple I1 for connection with a pipe line I8 leading to a source of vacuum, preferably the intake manifold I9 of the vehicle engine. The casing section I2 is provided with a connection 2| to which is attached a pipe 22 through which pressures in the chamber are controlled in a manner to be described.

The casing section adjacent its free edge is flared outwardly as at 25 to form a shoulder beyond which the casing section is substantially cylindrical as at 26. The diaphragm I3 is provided with a peripheral bead 21 seating against the shoulder 25. The casing section I2 is provided with a cylindrical portion 29 and at the inner extremity of such portion, the casing section I2 turns outwardly as at 38 and then extends cylindrically as at 3| to form a casing portion lying within and contacting with the bead 21. At its periphery, the casing section I2 is provided with an outstanding annular flange 32 lying against the edge of the bead 21.

At spaced points therearound, the casing portion 26 is angularly slotted as at 35 to provide circumferentially extending lips 36. After the parts are assembled in the positions shown in Figure 1 (and in Figure 3 referred to below) the free ends of the lips 36 are bent inwardly slightly to act as retainers for the casing section I2, these lips engaging the annular flange 32. As will become apparent below, the pressure in the chamber I5 never exceeds the atmospheric pressure against the outer face of the casing section I2, and accordingly the lips 36 act eiliciently as retaining means to flx the casing sections and dial phragm relative to each other. Attention is invited to the fact that the lips 36 present their edgewise strength against the ange 32 and thus provide more than adequate strength to retain the parts assembled.

A diaphragm plate 48 is arranged in contact with the body of the diaphragm I3 as shown in Figure 1. This diaphragm is fixed to a piston rod 4| by means of retaining discs 42 and 43, the former of which engages an annular shoulder 44 on the piston rod and the latter of which engages a retaining snap ring 45. 'I'he piston rod 4| carri a piston to be referred to later. A spring 46 engages the diaphragm plate 48 to tend to hold it in the normal off position shown in Figure 1 and return it to such position when released.

A preferably cast body 58 is arranged adiacent and coaxial with the casing section and is secured thereto by screws 5|, a gasket 52 being interposed between the elements as shown The bochr 58 is provided therewithin with a cylinder 54 divided by a piston 55 and its seal 56 to form a high pressure chamber 51 and a low pressure control chamber 58. 'I'he piston 55 and seal 56 are carried by the piston rod 4|. The end of the high pressure end of the cylinder 54 is provided with a plug 68 into which is tapped a pipe line 6|. This pipe line, in turn, is tapped into a pipe line 62 leading to the brake cylinders indicated by the numeral 63. These are the conventional brake cylinders of a motor vehicle and need not be illustrated or described in detail.

The piston rod 4| extends through a bearing block 65 and then through a floating bearing 66 flanged on opposite sides by seals 61 and 68, the former of which is seated against a disc 69 engaging a shoulder in the adjacent end of the cylinder 54. These seals 61 and 68 efficiently seal the chamber 58 against leakage of fluid around the piston rod 4| into the motor chamber I4. Attention is invited to the fact that pressure in 4 the chamber 58 is always low, and accordingly there is very little tendency for any leakage to occur.

The chamber 58 communicates through a port 15 with a. chamber 16 in which is arranged a diaphragm 11 surrounding the stem 18 of a disc 19. Referring to Figure 4, it will be noted that the diaphragm 11 seats against a shoulder 82 formed at the upper end of a cylindrical opening 63 of larger diameter than the chamber 16. The diaphragm is provided with a downturned edge 84 arranged against the wall of the opening 83. A clamping ring 86 is provided for the diaphragm 11 and is arranged in the cylindrical opening 83 and engages the bottom of the flange 84. The ring 85 is provided with an annular flange 81 lying within and engaging the flange 84. The ring 86 is held in position by a split retaining ring 88. Thus the diaphragm 11 is firmly fixed at its periphery, and the central portion of the diaphragm is movable downwardly under the influence of hydraulic fluid flowing into the chamber 16 through port 15 (Figure l).

The upper end of the stem 18 is provided with a head 98 engaging the central portion of the diaphragm 11 whereby such central portion is fixed with respect to the stem 18 and disc 19. The disc 19 is provided with a lower depending stem 82 having a reduced lower end 93 forming with the stern 92 a shoulder 94 for a purpose to be described. The lower end of the reduced stem 93 slides in a guide 95 xed to a bottom plate 86 fixed by screws 91 to the body 58. This body is provided beneath the disc 19 with an enlarged chamber 98 of which the plate 86 forms the bottom wall.

The casing section is ported as at |88 to afford communication between the motor chamber I4 and a passage |8I. A ported valve seat |82 is adapted to afford communication between the chamber 98 and passage |8| under the control of a downwardly seating vacuum valve |83. The stern |84 of this valve has loose engagement with one end of a valve operating lever |66, the opposite end of which engages a ball valve |81 normally closing a passage |88 leading to the atmosphere preferably through a conventional air cleaner (not shown). 'I'he reduced stem portion 93 (Figure 4) extends loosely through the lever |86. A leaf spring I I8 engages the lever |86 substantially closer to the valve |81 than to the valve |83, and the guide 95 serves to anchor one end of the spring ||8 as shown in Figures 1 and 4. The spring ||8 urges the lever |86 upwardly to normally seat the valve |81 and normally unseat the valve |83. A nipple ||2 is fixed to the plate 96 and serves to establish communication between the chamber 98 and the pipe 22. Thus the pressure in the motor chamber I5 is established in accordance with pressures in the chamber 98.

Fluid is supplied to the chamber 68 through a pipe line ||5 leading from a special master cylinder indicated as a whole by the numeral ||6 and illustrated in detail in Figure 2. This master cylinder comprises a cylinder body ||1 having a. cylindrical bore ||8 therein. A piston I|9 is movable in the bore ||8 through operation of the conventional rod |28 connected to the brake pedal |2| (Figure 1). The plunger ||8 has a seal |23 at its outer end and the plunger is limited in its outward movement by engaging a stop |24 backed up by a snap ring |25.

At its other end, the plunger I |9 is provided with an annular ange |28 slidable in the bore ||8 and apertured at as |28 for a purpose to be Vthrough a port |4|.

trol chamber 58.

described. The flange |28 engages one side of a seal |30, the opposite side of which engages a small annular flange |3| formed on the plunger H9. The ilange |28 and seal |30 divide the bore H8 into a pair of chambers |33 and |34, the former of which communicates with the master cylinder reservoir through a port |36.

A second plunger |38 is arranged in the bore H8 and has a reduced end |39 slidable in a bore |40 formed in the adjacent end of the plunger yH9 and communicating with the chamber |33 The reduced plunger end |39 forms on the plunger 38 a shoulder |43. A Wave Washer |44 is arranged between the shoulder .|43 and the adjacent end of the plunger H9 to urge the plungers H9 and |38 in opposite directions for a purpose to be described.

. The plunger |38 is provided with an axial passage |48, one end of which is enlarged as at |40 and the other end of which communicates with the chamber |40. A valve plunger` is arranged in the enlarged passage portion |49 and has a conical end |5| engageable in the adjacent -end of the passage |48.

A hollow plug |53 is threaded in the end of the cylinder body |1 adjacent the valve plunger |50. The inner end of this plug engages a seal |54 backed up by a ring |55 xed in position by va snap ring |56.

A spring |58 in the plug |53 urges the valve plunger |50 toward closed position. Movement of the valve plunger is limited by engagement of a washer |59 carried thereby, with a snap ring |60. The plug 53 has therein a chamber |62 in which the spring |58 is arranged, and the chamber |62 is ported as at |63 for communication -With the pipe line 62 (Figure l).

The chamber |34 is similarly ported as at |65 for communication with the pipe line I5 leading to the con- It will become apparent that the relatively small effective area of the plunger |38 operating in the chamber |62 generates a relatively high manually developed pressure While displacing a relatively small volume of fluid which is insufficient for moving the brake shoes into engagement with the drum. The fluid displaced from the chamber 34 operates the booster motor to supply the necessary additional volume of iluid to the brake cylinders, as described in detail below.

The form of the invention previously described makes use of a special master cylinder for displacing fluid from the chambers |34 and |62 for the purposes generally stated above. The form of the invention shown in Figure 3 is adapted for use with a conventional master cylinder and varies from the form of the apparatus shown in Figure l only by the addition of the means added thereto to supply functions corresponding to the operation of the plunger |9 for displacing fluid from the chamber |34 of Figure 2. Only such additional means in Figure 3 need be described, the remaining parts being identical with the parts previously described and indicated by the same reference numerals.

In the form of the invention shown in Figure 3, the numeral |10 designates a conventional master cylinder as a whole, the modied form of the invention being designed for use with such master cylinder. rod |12, operates the conventional piston (not shown) to displace fluid through a pipe line |13. The master cylinder includes the usual reservoir |14.

In Figure 3, a different body |16 is employed The usual pedal |1|, through a s in place of the body previously described. The motor, plunger and valve mechanism are identical with the corresponding parts previously described and have been indicated by the same reference numerals as in Figure 1. The body |18 is enlarged to provide for a cylinder |11, preferably corresponding in displacement with that of the usual master cylinder. The body |16 further includes a cylinder |18 of smaller diameter for the generation of relatively high pressure, as described below.

A piston |80, provided with a seal |8l, is arranged in the cylinder |11 and divides it into a. pair of chambers |82 and |83. The piston |80 is provided with a preferably integral cylindrical axial projection |84` having an annular enlargement |85 provided with a seal |86, forming 'a piston operable in. the cylinder |18. The piston |85 provides in the cylinder |18 a chamber y|81 which communicates with the chamber 51 through a passage |88. This passage, as will become apparent, corresponds to the pipe 6| (Figure 1) l previously described, and in view of the elimination of this pipe, the end of the cylinder 54 is plugged as at |89. The chamber |81 communicates with the wheel cylinders |92 through a suitable pipe line |93.

The pipe |13, connected to the master cylinder |10, leads to a port |95 and communicates therethrough with the chamber |82 for the flow of fluid into such chamber to move the piston |80 to the right as viewed in Figure 3. A return spring |96 urges the piston |80 toward the left, thus tending to keep this piston in the normal position shown in Figure 3.

As previously stated, the axial projection |84 is substantially cylindrical, being provided with an axial passage 200 reduced at the left hand end, as Viewed in Figure 3, to form a valve seat 20| engageable by a ball valve 202 urged toward closed position by a spring 203 which is weaker than the spring |96. A plug 204 in the cylinder |11 limits movement of the piston |80 to normal position and is provided with an axial projection 205 to unseat the ball 202 when the parts are in oli position. The plug 204 is grooved as at 206 to receive an O-ring 201 to seal the plug 204 against leakage. The plug 204 seats against the adjacent wall of the casing section to be held in position thereby when the parts are assembled.

The valve mechanism in Figure 3 may be identical with that described in connection with Figure l. To supply to the chamber 58 and thus to the chamber 16 the duid necessary for operating the valve mechanism, a port 2|0 communicates between the chambers 58 and |83. To normally balance pressures between chambers 58 and |82 when the parts are in the off position shown, these chambers are adapted to communicate with each other through a port 2H adapted to .be closed by a valve 2|2. A small cam 2|3, adjustable on the piston rod 4|, is adapted to slightly unseat the valve 2 |2 when the movable parts of the fluid pressure motor reach the fully off positions.

The piston 55 and seal 56, when the apparatus is in operation, are subject to relatively high pressures in the chamber 51 and t0 relatively lower pressures in the chamber 58. Accordingly, pressure differentials exist on opposite sides of the motor-operated piston and very slight leakage will occur past the piston. Since the piston is not subjected at one side to substantial hydraulic pressures and at its opposite side',` to

7 vacuum in the chamber |4, the leakage neces'- -sariiy will be very slight, and the loss of uid into the vacuum chamber I4 is further reduced by means of the seals 61 and 66. However, any duid leaking past the seals 61 and 68 may be recovered and returned to the reservoir |14. For this purpose. a small chamber ZIG is provided `adjacent the seal 66, and any fluid leaking into this chamber will drain therefrom by gravity throh a small passage 2|1. The passage |0| described in connection with Figure 1 is provided in Figure 3 -with a downwardly recessed chamber 2li into which the leakage fluid from passage 2I1 will iind its Way. The chamber 2|6 h connected to the reservoir |14 by a pipe 2|0 in which is interposed a small pump 220 and a check valve 22|.

' Operation The form of booster unit shown in Figure 1 is used in connection with the special type of master cylinder illustrated in Figure 2. The

parts normally occupy the positions shown in Figures l and 2. When the brakes are to be applied, the operator depresses the pedal III (Figure l) to move the reciprocable parts in Figure 2 toward the right. The piston |26 and seal |30 displace fluid from the chamber |04 through port |65 into the primary or low pressure chamber 56 (Figure l). At the same time,

the plunger |56 dlsplaces fluid from the chamber |62 by moving thereinto. The fluid thus displaced ilows through port |63 and thence through pipe line 52 to the brake cylinders. At this point, attention is invited to the fact that the arrangement referred to provides two -manually operated fluid displacing means. As will become apparent, duid from the chamber |34 meets a very low degree of resistance and accordingly remains at low pressure, thus in itself offering little resistance to movement of the brake pedal. The plunger |36 being of relatively small diameter, the operator may, without great effort, develop a relatively high pressure in the chamber |62, brake lines 62 and brake cylinders 63. The small plunger |36 is capable of developing relatively high pressure, as stated. Conversely, this plunger is incapable of displacing fluid in suillcient quantity, within the limits of its travel, to effect movement of the brake shoes into engagement with the drums and to apply the brakes fully. The additional fluid required for this purpose is supplied from the chamber 51 (Figure rl) through pipe 6| through the operation of the uid pressure operated motor.

Fluid displaced from the low pressure chamber |34, flowing through pipe II5, enters chamber 56 and then flows through port 15 into valve control chamber 16 (Figures l and 4) to urge the diaphragm 11 and stem 92 downwardly. This action transmits movement to the valve operating lever |06 intermediate the ends thereof, the left hand end of this lever as viewed in Figure l moving downwardly while the lever fulcrums on its point of contact with the ball valve |01. Very slight movement of the lever |06 in this manner drops the valve |03 on its seat, thus disconnecting the passage IOI from the chamber 98. When the valve I 03 closes, no further downward movement of the left hand end of the lever |06 can occur, and further downward movement of the diaphragm 11 and stem 92 e'ects downward movement of the right hand end of the lever |06 against the tension of the spring ||0 releasing the ball valve |01 from its Rat.

iii)

The motor Il is normally vacuum suspended. The chamber |4 is in nxed communication with the intake manifold and also is in constant communication with the passage III. The valve |01 being normally closed and the valve |03 being normally open, vacuum will be communicated through passage |02. chamber 96 and pipe l! to the motor chamber I5, thus vacuum suspending the diaphragm Il.

The closing of the valve |03 cuts of! communication between the motor chamber I5 and the vacuum chamber I4 and opens communication between the chamber Il and the atmosphere through passage |08. Thus air is admitted into the motor chamber Il to move the diaphragm I3 toward the right together with the parts connected thereto. Movement therefore is imparted to the piston 55 to displace iiuid from the chamber 51 to lines 0| and 02 into the brake cylinders. This fluid, together with the fluid displaced by the plunger |30 (Figure 2) supplies the necessary quantity ot hydraulic fluid for movement of the brake shoes, thus permitting the use of a small plunger |30 through which greater pressure can be developed through the same pedal edort. thus vpermitting the present device to generate In the chamber |62 the braking pressures to which the wheel cylinders 63 will be subjected.

As the piston 55 moves to the right, the capacity of the chamber 58 will expand, and this operation continues so long as fluid is delivered to the chamber 58 from the master cylinder chamber |34. As soon as movement of the pedal |2| is arrested, no more fluid will ilow into chamber 50, and a very slight expansion of the chamber 50 by movement of the piston l5 will result in the return movement of the diaphragm 11 to normal position, or at least to a position in which the bali |01 will be seated to prevent the admission of further air into the motor chamber I5. Thus a perfect follow-up action is provided without the presence of substantial pressures against the parts which operate the valve mechanism, and without operating such mechanism in accordance with relative mechanical movement of the parts. This has been found to be highly advantageous for several reasons. In the rst place, the follow-up action is more accurate and instantaneous without noticeable fluctuations in pressure in the pipe lines, and thus the operator is prevented from feeling through his foot the cutting in and out of the booster motor. Moreover, the operator gets a more accurate feei" at all times since the full braking pressure always reacts on the operators foot through pressures exerted on the plunger Ill. This plunger being substantially smaller than the plungers of conventional master cylinders, pressures may be developed to a relatively high point directly by the operator, who always feels a reaction in exact proportion to brake application.

When the operator releases his foot from the pedal IZI, the spring |50, assisted by the pressure of the fluid in the brake lines, will move the plunger |38 and associated elements back to their normal positions as shown in Figure 2. Expansion of the chamber |34 withdraws tluid from the chamber 50 as the piston 55 moves toward the left in Figure 2. the valve mechanism now occupying the normal motor-deenergizing position. The chamber 66 will be cut of! from communication with the atmosphere by the closing of the ball valve |01, while the motor chamber i5 will be placed in its normal communication with the motor chamber I4 past valve |03. Movementl of the motor parts to off positions will be accomplished by spring 46 and pressures acting against the piston 55 by fluid in chamber 51.

The plunger I I9 is liimted in its movement to off position by the stop ring |24. When such off position is reached, the valve rI| will be closed with the disc |59 engaging snap ring |60. The engagement of the latter two elements does not provide a completely leak-proof joint. The closing of the` valve |5|, however, prevents fluid leaking past elements |59 and |60 from entering the passage |48 and thus returning to the reservoir |35. Accordingly, the proper residual pressure is maintained in the brake lines. If, through expansion, pressure in the brakes should increase, the increased pressure will act on the right hand end of plunger |38 to move it slightly toward the left in Figure 2 against the tension of the wave washer |44. Since the valve |5| remains stationary, fluid will leak into the passage |48 until pressure in the chamber |62 drops to the desired residual pressure. The washer |44 will then urge the plunger |38 toward the right the slight distance necessary to close the valve |5I. through port |29 toward the right in Figure 2 around seal |30 to satisfy any fluid deficiency in the chamber |34, and fiuid may leak in the same manner and for the same purpose toward the right around seal |54 into chamber |62.

The form of the invention shown in Figure 3 is intended for use With a conventional master cylinder as diagrammatically represented by the numeral |10. The master cylinder has the usual piston which displaces fluid upon operation of the brake pedal, and this iluid flows throughv line |13 into chamber |82 tomove the pistons |80 and |85. Here again is provided a pair of pistons, one of small area (|85) to develop braking pressures, and the other a large piston (|80) to displace fluid for the purpose of operating the control valve mechanism for the fluid pressure motor. The uid in the line |13 and chamber |82 thus forms, in effect, a hydraulic link between the master cylinder a-nd the dual piston fluid displacing means, such means therefore comprising a manually o-perable mechanism in the same manner that this is true of the plungers I'StA and |28 (Figure 2).

Fluid moving into the chamber |82 operates the pistons |80 and |85, the latter of which, because or" its relatively small area, displaces a relatively small volume of fluid at relatively high pressure from the chamber |81 into the brake cylinders. The insufiicient quantity of brake iluid thus provided for moving the brake shoes is made up, as in the previous case, by fluid from the chamber 51.

Movement of the piston |80 displaces iluid from chamber |83 through port 2|0 into chamber 58 and thence into the valve operating chamber 16 to operate the Valve mechanism in the manner previously described. Energization of the motor I0 displaces iiuid from vchamber 51 through passage |88 into chamber |81 and thence through line |93 to the brake cylinders |92. The chambers y51 and |81 thus communicate with each other and with the brake cylinders to supply hydraulic liuid thereto, the piston 55'making up the lack in volume displaced by piston |85, the piston |85 being manually operated to determine the effective braking pressure of the fluidin the brake cylinders |92. Accordingly, the ap- Fluid from the reservoir may leak.

paratus in Figure 3 performs exactly the samefunctions as the apparatus in Figures 1 and 2.

The follow-up action of the valve mechanism is identical with that previously described and possesses the same advantages. The brakes are released by releasing the pedal I1I, the master cylinder parts returning to normal position in the usual manner and the spring |96 returning the pistons |60 and |85 to their off positions. When the piston |800 approaches its normal positionthe pin or stud 205 unseats the ball 202l against the tension of the spring 203, this spring Y being weaker than the spring |96, as will be apparent. When the parts are in the oi positions, therefore, the chambers |82 and |01 communicate with each other, thus establishing communication between the brake cylinders |92 and the master cylinder |10 whereby the residual pressure valve of the master cylinder retains the desired pressure throughout the system from the master cylinder to the wheel cylinders.

The diaphragm I3 and associated elements return to normal positions in the same manner as in Figure l. As the piston rod 4| approaches normal position, the cam 2I3 slightly lifts valve 2I2, thus establishing restricted communication between chambers 58 and |82 to maintain balanced pressures therein under all conditions whenv the brake is not in operation.

Leakage of fluid into the chamber 2I6 will be extremely slight. drip downwardly through passage 2 I1 into chamber 2 I8 to be returned to the reservoir |14. Pressure in the reservoir will be that of the atmosphere, while vacuum prevails at all times in the chamber 2|8. Thus the check valve 22| is provided, and if the parts are so located that the inertia of any brake fluid in the pipe 2|9 will open the check valve 22| sufficiently for the fluid to pass on into the reservoir, the pump 220 need not be employed. Otherwise, the use of the small pump 220 is necessary for returning leakage iiuid to the reservoir.

The casing structure, including the securingl lips 36, is highly advantageous. In devices of this character, the two casing sections usuallyv are secured with respect to each other and against opposite sides of a peripheral diaphragm bead by means of a split clamping band. The present construction eliminates the use of the clamping band and permits the motor to be easily and quickly assembled. It merely is necessary to `slip the diaphragm bead 21 over the casing ange 3|, and then move the two casings into the operative position shown. A pair of pliers then may be employed for bending the lips 36 inwardly to a slight extent over the flange 32. The elements are then securely fixed to each other, and the edgewise rigidity of the lips 36 eliminates any possibility that the casing sections may become disengaged. If necessary for disassembling thek motor, the lips 36 need be merely bent slightly outwardly to clear the flange 32 whereupon the casing section l2 may be removed.

I claim:

1. In a braking system having wheel cylinders to apply brakes, means operated by manual power to transmit hydraulic fluid directlyl to the wheel cylinders to apply the brakes, a booster comprising uid displacing means, a power operated motor mechanism connected to said uid displacing means to operate it and force hy' draulic uid to said wheel cylinders to augment the amount of fluid transmitted by said means operated by manual power, low pressure fluid dis- Any such uid, however, will placing means connected to and operable in unison with and by said means operated by manual power to transmit a proportionate volume of control fluid, means comprising a control chamber, in said booster to receive said volume of control fluid, and follow-up control means responsive to the volume of control fluid in said control chamber to control the power of said motor mechanism to provide a follow-up action of said fluid displacing means with said means operated by manual power to augment the fluid transmitted to the wheel cylinders in proportion to the fluid transmitted thereto by said means operated by manual power.

2. In a braking system having wheel cylinders to apply the brakes, a pair of connected simultaneously manually operable fluid displacing devices one of which is connected to the wheel cylinders to apply the brakes, a fluid displacing mechanism connected to the wheel cylinders to augment the amount of fluid transmitted thereto by said one fluid displacing device, a differential fluid pressure operated motor connected to said fluid displacing mechanism, a valve mechanism normally biased to deenergize said motor, an expansible chamber device, comprising a control chamber, connected to said valve mechanism, means establishing communication between said control chamber device and the other of said fluid displacing devices whereby fluid displaced from the latter device expands the volume of said control chamber and energizes said motor, and means operable by said motor for expanding said fluid communication means to reduce the volume of said control chamber to tend to prevent a vmotor-energizing operation of said expansible chamber device whereby said motor is caused to operate said fluid displacing mechanism in a follow-up action relative to said one fluid displacing device.

3. In a braking system having wheel cylinders to apply the brakes, a pair of connected simultaneously manually operable fluid displacing devices one of which is connected to the wheel cylinders to apply the brakes, a cylinder, a piston in said cylinder dividing it into a control chamber and a high pressure chamber, the latter Iof which communicates with the wheel cylinders to augment the amount of fluid transmitted thereto by said one iluid displacing device, a power device connected to said piston, control means for said power device normally biased to deenergize said power device, said control Imeans comprising an expansible chamber communieating with said control chamber and expansible to energize said power "device, and means establishing communication between the other of said fluid displacing devices and said control chamber, said control chamber expanding upon energization of said power device to tend to prevent expansion of said expansible chamber.

4. In a braking system having wheel cylinders to apply the brakes, ya pair of connected simultaneously manually operable fluid displacing devices one of which is connected to the wheel cylinders to apply the brakes, a cylinder, a piston in said cylinder dividing it into a control chamber and a high pressure chamber, the latter of which communicates with the wheel cylinders to augment the amount of fluid transmitted thereto by said one fluid displacing device, a differential fluid pressure operated motor connected to Vsaid piston, a control valve mech'- anism for said motor normally biased to deenerglze said motor, an expansible 'chamber de- 12 vice communicating with said control chamber and expansible to operate said valve mechanism and energize said motor, and means communicating between said control chamber and the other of said fluid displacing devices, said control chamber expanding during energization oi' said motor to tend to prevent expansion of said eirpansible chamber device.

5. In a braking system having wheel cylinders to apply the brakes, a master cylinder comprising a larger cylinder and a smaller cylinder, a larger plunger and a smaller plunger operable respectively in said larger and smaller cylinders, said plungers having fixed mechanical connection with each other'` and being manually operable, s'aid smaller cylinder being directly connected to the wheel cylinders to apply the brakes, a fluid displacing mechanism communicating with the wheel cylinders to augment the amount o'f 4fluid transmitted thereto from said smaller cylinder, a power device for operating said fluid displacing mechanism, and means operable by fluid displaced from said larger cylinder for controlling said power device.

6; In a braking system having wheel cylinders to apply the brakes, a master cylinder comprising a larger cylinder and a Smaller cylinder, a larger plunger and a smaller plunger operable respectively in said larger and smaller cylinders, said plungers having fixed mechanical connection with each other and being manually operable, said smaller cylinder being connected to the wheel cyl-inders to apply the brakes, a cylinder, a piston in such cylinder dividing it into a high pressure chamber and a control chamber, said high pressure chamber communicating with the wheel cylinders to augment the amount of fluid transmitted thereto from said smaller cylinder, a fluid pressure operated motor connected to said piston and energizable to displace fluid from said high pressure chamber and yincrease the capacity of vsaid control chamber, a control valve mechanism for said motor, an expansible chamber device connected to `said valve mechari-ism and expansible 'to energize said motor, said expansible chamber device communicating with said control chamber, and means for connecting said larger cylinder to said control chamber.

7. Apparatus constructed in accordance with claim 6 wherein 'said larger and smaller plungers are in axial alignment `and are axially relatively vvvmovable, resilient means urging said plungers away from Veach other, a reservoir `communicating with said larger cylinder, said smaller plunger having an axial passage therethrough from Vsaid larger cylinder to said smaller cylinder, and a valve seating in the end of said axial passage communicating with said smaller cylinder when said smaller plunger is in its off" position, said valve being mounted to travel with said smaller plunger.

8. In a braking system having wheel cylinders to apply the brakes, la manually operable master cylinder, a. booster mechanism comprising a booster cylinder, a piston therein dividing it into a high pressure chamber and a control chamber, a second cylinder, an actuating piston in said cylinder dividing it into an inlet chamber and a low pressure chamber the latter of which communicates with said control chamber, said master cylinder communicating with said inlet chamber whereby fluid displaced irrto such chamber from the master cylinder moves said actuating piston to displace fluid into Vsaid control chamber, a relatively small cylinder 'in axial alignment with said second cylinder, a relatively small plunger in said relatively small cylinder connected to said actuating piston, said relatively small cylinder communicating with .the wheel cylinders and with said high pressure chamber, a power device connected to the piston in said booster cylinder, and a control mechanism for said power device comprising an expansible chamber device communicating with said low pressure chamber and expansible to energize said power device.

9. In a braking system having Wheel cylinders to apply the brakes, a manually operable master cylinder, a booster mechanism comprising a booster cylinder, a piston therein dividing it into a high pressure chamber and a control chamber, a second cylinder, an actuating piston in said cylinder dividing it into an inlet chamber and a low pressure chamber the latter of which communicates with said control chamber, said master cylinder communicating with said inlet chamber whereby fluid displaced into such chamber from the master cylinder moves said actuating piston to displace fluid into said control chamber, a relatively small cylinder in axial alignment with said second cylinder, a relatively small plunger in said relatively small cylinder connected to said actuating piston, said relatively small cylinder communicating with the Wheel cylinders and with said high pressure chamber, a iuid pressure operated motor connected to the piston in said booster cylinder, a control valve mechanism for said motor biased to deenergize said motor, and an expansible chamber device connected to said valve mechanism and communicating with said 14 low pressure chamber to be expanded by uid therefrom to energize said motor.

10. Apparatus constructed in accordance with claim 9 wherein said actuating piston and said relatively small plunger are provided with a passage communicating between said inlet chamber and said relatively small cylinder, a valve in said passage biased to closed position to cut off communication therethrough, and means engaging said valve when said actuating piston is in oil position for opening said valve.

1l. Apparatus constructed in accordance with claim 9 provided with a port connected between said inlet chamber and said control chamber, a valve normally closing said port, and means operable by said uid pressure motor when the latter is in its off position for yopening said valve.

WILLIAM STELZER.

References Cited in the le 0f this patent UNITED STATES PATENTS Number Name Date 1,834,368 Arbuckle Dec. 1, 1931 2,057,707 Carroll Oct. 20, 1936 2,115,438 Wolf Apr. 26, 1938 2,206,976 Rossmann July 9, 1940 2,322,063 Schnell June 15, 1943 2,328,687 Freeman Sept. 7, 1943 2,352,357 Almond June 27, 1944 2,353,755 Price Ju1y 18, 1944 2,429,195 Price Oct. 14, 1947 FOREIGN PATENTS Number Country Date 835,760 France Oct. 3, 1938 

